Tires very Strange....

[Delaine and Lindy]

We moved out of Buena Vist Colorado yesterday and traveled over Rt 24 and over some 9,000' + passes. We departed with the tires 17.5" G114 Goodyears at he side wall pressure of 125 lbs. Well when we got just east of Colorado Springs the Pressure Pro went off, and the tire pressure was a 140lbs??? Stopped and lowered the pressure to a 120lbs, tire were warm and I know you should add air when their cool, however the alarm we off and didn't come back on. We stopped at the KOA in Goodland Kansas and this morning, the PP alarm was beeping?? The pressure in the tires was 95 lbs?? We have never had this issue before. In the past we ran 16" Goodyear G614 and traveled in the same places? So with the 17.5's this is Strange... Has anyone had this issue... The 17.5's have about 14,000 plus or minus miles.. Happy Trails....

[Art-n-Marge]

If you departed when the tires were at 125 psi, they were already too high. They should have been "bled" to 110 psi prior to departing especially if you gain more altitude. The higher the altitude the higher the pressure would get and this is why the alarm went off. Then you let 25 lbs of pressure out when the tires were hot to prevent the alarm from going off.

While this is a good idea if your tires are too high already, you may have let out TOO much air. Keep in mind hot tires at 120 will go below that when they cool off, like what you stated when they got to 95 lbs at the lower altitude. Maybe you should have considered reducing the psi to 130 to adjust for this especially if you were going to get to a lower altitude. This doesn't guarantee that they would still be at 110 psi, but it's something to think about.

I'm just guessing here but from the little I know about tires, the psi and the amount of air inside can be affected by altitude, temperature/climate) and pressure, so a 17.5" tire will have a lot more air affecting the tire than a 16" tire assuming the 17.5" tire is also larger in overall size. I find this with my auto as well. They have less air volume even being 19" diameter and are less impacted by altitude, climate and pressure compared to my larger truck and trailer tires because the size of these 19" tires are smaller than the 17" tires on my truck AND the 16" tires on my trailer. Don't forget to consider that the diameter of the tire bead does not mean there is MORE air volume. I hope I explained this reasonably well. In summary, the greater the volume of air, the more it's affected as altitude, temperature and pressures change. This is why nitrogen is becoming more and more popular since it isn't as affected as much as oxygen molecules. I wish I could find the internet links that explained this so well.

This is why it's good you have the Pressure Pro. It HELPS create the necessary consciousness of what's going on with those all important rubber pads on the ground, especially when you are at the exremes of distance, altitude and weather! I don't have one so I have to be extra diligent.

[Waynem]

For every 10 degrees of ambient temperature change there will be a 2% change in air pressure. For every 1000 feet of altitude, there will be a .48 (point four eight) change in psi. Combine both altitude and ambient air temperature for inflation changes.


In you original post, you stated 125 psi, and again I'm assuming it is for the 215/17.5(h) tire. That inflation of 125 psi. As you dropped in altitude, you also most likely experienced an ambient temperature increase.

ALL of these measurements should be done with a cold tire. When you start adding road heat, breaking/stopping heat, etc., you are going to see a markedly increase in tire pressure. I don't thing 15 pounds of difference between 125 and 140 is that much of a difference regarding heat.

On the other hand, dropping down to 95 psi could have damaged the tires. Depending on the rated weight on the tire, you could have been below the 20% margin designed by Goodyear. You should have the tire inspected.

My very personal opinion is that you should not have let the air out when it was at 140 psi until you could reach a full cold state on the tire, but then, that is my opinion.

Here is a link to GoodYear RV tire guide.

A quote from their site:
"Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire. Trailer tires experience significant lateral (side-to-side) loads due to vehicle sway from uneven roads or passing vehicles. Using the inflation pressure engraved on the sidewall will provide optimum load carrying capacity and minimize heat build-up"

So your inflation to sidewall pressures is correct according to Goodyear.

Good luck, and check the tire that was at 95 psi.